With most plastic water bottles, the cap body is made from a rigid or semi rigid material and the nozzle valve is made from a semi rigid semi flexible material. Typically, the material from which the cap body is made has a greater thermal linear expansion than the material from which the nozzle body is made. As a result, the nozzle valve can experience creep in size over time when subject to relatively extreme thermal conditions and hermetic or hydraulic sealing can be lost. As used herein, the terms hermetic and hydraulic are interchangeable. Creep can also result from mechanical events or the combination of thermal and mechanical events.
As here, where the nozzle body and cap body have different thermal linear expansion coefficients, hot and cold events or conditions are both relevant and, depending upon how parts interface, give rise to different issues of creep. Similarly, mechanical expansion and compression forces can give rise to creep. As compared to the cap body, the phenomenon of creep has a greater effect on the nozzle body due to the properties of the semi rigid semi flexible material from which it is made. Expanding or compressing a nozzle valve over time can cause the shape or size of the nozzle body to expand or contract. Further still, the process of creep is accelerated at elevated temperatures and humidity levels, for example, those that occur during a typical dishwasher cleaning and drying cycle. When coupled with mechanical expansion or compression forces acting on a nozzle body, elevated temperatures can drive creep to its mechanical limit altering the size or shape of the nozzle body. Conversely, reduced temperatures, experienced for example when a water bottle is placed in a freezer or when it is filled with relatively cold fluids, are less likely to result in creep because the nozzle body will stiffen and resist the effects of compression. Nonetheless, creep can still be a factor in reduced temperature conditions. In addition, stress can be molded into a component piece, particularly an injection molded part. Exposure to elevated temperatures can release such built-in stress. Often, such stresses cause a part to shrink. Any change in the shape or size of a part that is integral in forming a fluid seal can have a detrimental effect on the seal.
Typically, with current water bottles, when a nozzle valve and cap body are new, there is a press fit between mating parts that cause the semi rigid semi flexible valves to stretch and or compress to form hermetic seals by pressing against the mating surfaces of the cap body. If the parts are left in a stretched and or compressed condition for a period of time and subjected to relatively heightened thermal conditions, for example the wash/dry cycle of a dishwasher, the semi flexible semi rigid nozzle valve will deform or creep to the shape and the size of the mating surfaces of the relatively rigid cap. The net result is that the sealing surfaces lose their ability to press tightly against one another. In one state, the mating geometries are sized identically to one another. Parts that are sized identically will still form a hermetic seal provided the axial and radial alignment between parts does not change. However, when the nozzle valve is toggled from the open to the closed position, the parts will no longer have the same alignment and, therefore, will not form a hermetic seal. In a second state, the mating geometries have changed and the nozzle valve is larger than the mating surface of the cap body. As a result, the ability to form a hermetic seal between the mating parts is lost, regardless of the axial position of the parts.